As is well known in the art, a number of divided cannulas are currently available on the market which assist with both supplying a desired treatment or insufflation gas, such as oxygen, to the patient via a first insufflating nare of the nasal cannula and also facilitates detection of a desired exhaled gas, such as carbon dioxide, via a second sampling nare of the nasal cannula. U.S. Pat. Nos. 5,335,656 and 6,655,385 are examples of two currently known exemplary divided cannulas and the teachings and disclosures of both of those references are incorporated herein by reference in their entireties.
While the prior art designs provide a significant improvement over the prior art, there still remain a number of issues that need to be addressed. Specifically, it was discovered that with prior art cannulas, the amount of oxygen being supplied to the patient did not equal the amount of oxygen actually being absorbed into the bloodstream of the patient. In order to increase the oxygen level within the bloodstream, it was necessary to increase the supply of oxygen to the patient beyond the ‘required’ amount. It was also found that administering more oxygen to the patient typically resulted in greater dilution of the end-tidal exhalation gases. Such dilution adversely effects detection of the amount of end-tidal CO2 within the end-tidal exhalation gases of the patient thereby skewing the accurate analysis.
While such nasal cannulas have perform relatively satisfactorily, there still is a need for improving collection of a substantially undiluted sample of the end-tidal exhaled gases, and detection of the amount of carbon dioxide contained in the end-tidal exhaled gases of the patient so that such reading more accurately reflects the actual amount of dissolved CO2 contained within the bloodstream of the patient. In addition, a relatively low flow rate of oxygen, which adequately sustains the highest level of dissolved oxygen in the blood of the patient, is also desirable so as to minimize the effect that any excess oxygen, supplied to the patient, can have on the collected and measured end-tidal CO2 gases during the time period that the patient is connected with the nasal cannula.
It is desirable to deliver supplemental oxygen to a patient in order to sustain a normal and desired level of dissolved oxygen within the bloodstream of the patient of 100 mmHg PaO2 (e.g., the partial pressure of dissolved O2). That is, the normal PaO2 for a person breathing 21% oxygen (typically found in air) at sea level is 100 mmHg. Accordingly, in the event that the PaO2 (i.e., partial pressure of dissolved O2) of the patient drops below 100 mmHg, then it is necessary to supply supplementary oxygen to the patient in order to increase the PaO2 of the patient to the desired level. Currently, a prior art divided cannula is utilized for supplying supplemental oxygen to the patient and such cannula typically has an oxygen flow rate of up to about 6 liters per minute.